Multiple computer systems often interact in order to achieve a goal, such as when an application program on a computer system interacts with other remote systems and applications in order to obtain various types of information and functionality that are not part of the application program. By performing such interactions, an application program may be able to leverage information and functionality from vast numbers of other computer systems over the Internet or other networks.
In order to enable such interactions between remote computer systems and executing software applications, various programmatic interaction mechanisms have been developed. For example, remote procedure call (“RPC”) protocols have long existed that allow a program on one computer to cause a program on another computer to be executed, and various object-oriented architectures such as CORBA (“Common Object Request Broker Architecture”), DCOM (“Distributed Component Object Model”), Java RMI (“Remote Method Invocation”), JavaSpaces, Jini, JXTA, and UPnP (“Universal Plug-n-Play”) provide similar capabilities. In addition, a variety of middleware programs have been implemented to connect separate applications (often of distinct types and from unrelated sources) to allow communication. For example, various EDI (“Electronic Data Interchange”) networks exist that provide standard mechanisms to allow a computer system of one user of the network to send data to a computer system of another user of the network.
The widespread popularity of the World Wide Web (“Web”) has provided additional opportunities for computers to inter-communicate. For example, much current Web use involves users interactively requesting Web pages from Web servers (e.g., via executing Web browser applications of the users) and receiving the requested information in response. In addition to such interactive user specification of requested information, there is also growing use of the Web to support the programmatic interaction of remote applications to exchange information via defined APIs (“application program interfaces”), such as APIs based on Web services interaction mechanisms. Web services allow heterogeneous applications and computers to interact, and can be defined and implemented using a variety of underlying protocols and techniques. For example, some Web service implementations return data in XML (“eXtensible Markup Language”) format using HTTP (“HyperText Transport Protocol”) in response to a Web service invocation request specified as a URI (“Uniform Resource Identifier”), such as a URL (“Uniform Resource Locator”) that includes a specified operation and one or more query parameters. In other implementations, additional underlying protocols are used for various purposes, such as SOAP (“Simple Object Access Protocol”) for standard message exchange, WSDL (“Web Services Description Language”) for description of service invocation interfaces (e.g., using XML format), and UDDI (“Universal Description, Discovery, and Integration service”) for discovery of available services.
Interactions between computer systems and software applications may be performed for a variety of reasons. For example, Web use has increasingly provided a medium for users to interactively engage in shopping-related transactions, and interactions between computer systems may further be performed as part of a variety of other types of transactions between two or more parties, such as for other commerce-related transactions that involve the exchange of funds between the parties. With respect to shopping-related transactions, the Web allows users to search for and order items (such as products, services and/or information) that are available for purchase, rent, lease, license, trade, evaluation, sampling, subscription to, etc. In many circumstances, a user can visit the Web site of a Web merchant or retailer (also referred to as a “Web store”) or other online or electronic marketplace that sells one or more items, and can view information about the items, give an instruction to place an order for one or more items, and provide information needed to complete the purchase (e.g., payment and shipping information). The Web merchant then fulfills the order by providing the ordered items to the indicated recipient, such as by providing product items that have been ordered through physical distribution channels (e.g., shipment via a governmental postal service or private common carrier) or electronically (e.g., via download over the Internet, such as for digital music or videos) as appropriate. Ordered service items may similarly be provided electronically (e.g., providing email service) or physically (e.g., performing cleaning services at the purchaser's house).
Information about transactions that have occurred often needs to be stored in a reliable manner for long periods of time (e.g., indefinitely), such as by a storage system that is accessible to other systems providing transaction information to be stored and/or retrieving stored transaction information. However, such storage system typically need to provide a high degree of availability to the other systems, particularly if high volumes of requests to the storage system occur, as well as to be able to scale efficiently to accommodate an increasing amount of stored transaction-related data and/or an increasing volume of transactions. Unfortunately, existing storage systems (e.g., a monolithic relational database system) cannot typically provide such storage-related capabilities in a cost-effective manner, and are not typically able to effectively scale to meet increasing demand.